An alleged radicalised neo-Nazi reportedly stockpiled weapons and plotted a mass-shooting at a NSW mall before being stopped by police two years ago.

Fairfax reports on Sunday that Michael James Holt, 26, recently pleaded guilty to several firearm-related charges after weapons, including homemade guns, were discovered by police at three properties across NSW in 2015, following a tip-off.

The alleged white supremacist reportedly wanted to commit an "indiscriminate public place shooting" and had considered Tuggerah Westfield on the central coast, a caller told Crime Stoppers according to the agreed statement of facts tendered in Penrith Local Court, Fairfax reports.

He had also told a school counsellor Adolf Hitler was "the greatest person to live" and posted pro-gun violence and anti-government rants online.

Holt, who is not believed to be associated with any far-right groups, is due to be sentenced in March.